At present, a D2D communication technology is available. In this type of communication mode, terminals (such as user equipment (UE)) can directly communicate with each other, which does not require forwarding by a base station (such as an evolved Node B (eNB)) and shares data load of the base station. Because D2D communication has only one hop and does not need an intermediate device, the D2D communication can better utilize a spectrum resource, improve spectrum utilization and a data rate, and also reduces load of a base station.
In order to improve spectrum utilization and maximize use of a radio-frequency capability of an existing terminal, a D2D communication link may share a target resource with an existing communications system. To avoid interfering with another terminal in the system, D2D communication does not use a downlink resource (a link from a base station to a terminal) of the communications system, but only reuses an uplink resource (a link from a terminal to a base station) of the communications system because an interference immunity of a base station is much stronger than that of a common terminal. There is a relatively high likelihood that two D2D devices perform communication by means of time division multiplexing on the uplink resource, which does not require support for simultaneous receiving or sending, and requires only that while one device sends data, the other device receives data.
In an existing communications system, a target resource for bearing a reference signal (RS) is fixed, for example, an uplink demodulation reference signal (UL DRS) is carried by two symbols (an example of the target resource), where the two symbols are separately located in the middle of each timeslot. Therefore, for transmission of an RS in a D2D communication link, a method for transmitting an UL RS in the existing communications system may be used, that is, transmission is performed using a symbol in the middle of each timeslot.
However, because a location of a symbol used to transmit an RS is fixed between two timeslots, when the number of terminal pairs that perform D2D communication is relatively large, there is a problem that resources for bearing RSs are insufficient.